I'm running v1.27.8747 ND Std on a WRT54GL v1.1 with Inactive Rules Cleaning activated. Trouble is, the entries never get deleted automatically. Skype stays around forever, as well as Pidgin, even well after the programs are closed in Windows. Even when the computers in question are completely shut down and/or disconnected from the router for 24 hours or more, the UPnP entries remain.

Am I misunderstanding how the inactive rules cleaning is supposed to work, by automatically deleting inactive UPnP entries after the indicated period of time, or no?

For the record, I've already re-flashed the firmware, even doing an NVRAM clear both before and after the flash. The router has been rebooted several times, including a power recycle, to no avail.

Until the cleaning threshold is reached, at 20 entries in the table, they won't be cleared. The fault is really with Skype that didn't close the port when it exited. Anyway, you can reduce the threshold :-)